Filariasis
Filariasis is a parasitic infection caused by threadlike worms that are transmitted through mosquito bites, particularly in tropical and subtropical regions. The adult worms reside in the lymphatic system and produce microfilariae, which circulate in the bloodstream. This disease is commonly known as lymphatic filariasis, especially when symptomatic. The transmission is facilitated by certain mosquito species, with Wuchereria bancrofti being the most prevalent causative agent in many areas, while Brugia malayi and Brugia timori are also significant in parts of Asia.
Individuals living in regions prone to mosquito exposure, lack of sanitation, and healthcare access are at higher risk for infection. Symptoms may include lymphedema—a painful swelling in various body parts—and can lead to severe complications like elephantiasis and mental health challenges. Diagnosis typically involves blood tests conducted at night, as microfilariae are more easily detected during this time. While treatment options are available to eliminate the parasites, management of symptoms is crucial, particularly for those with chronic conditions. Preventive measures focus on minimizing mosquito bites through protective clothing and sleeping arrangements.
Filariasis
- ANATOMY OR SYSTEM AFFECTED: Lymphatic system, tissue
- ALSO KNOWN AS: Lymphatic filariasis
Definition
Filariasis is an infection with microscopic, threadlike worms transmitted from person to person by repeated mosquito bites. Adult worms live and reproduce in the lymph system, producing microscopic worms known as microfilariae. These microfilariae circulate throughout the body's blood vessels. When a mosquito bites an infected person and moves on to the next person, the microfilariae are deposited into the skin and move to the lymphatic system. The disease is often called lymphatic filariasis, especially when symptoms occur.
Causes
The mosquito is the vector or disease-carrying insect that transmits filariasis from person to person. In Africa, the Anopheles mosquito is the most common vector. The Culex quinquefasciatus mosquito in the Americas and the Mansonia mosquito in Asia and the Pacific Rim transmit the infection.
Three species of worms cause lymphatic filariasis. Most infections are caused by Wuchereria bancrofti, but in Asia the infection filariasis is also caused by Brugia malayi and B. timori. The adult worms live up to seven years. Multiple mosquito bites over time are needed before symptoms of the disease occur. Symptoms can take several months to several years to appear.
Risk Factors
The most significant risk factor is living in a subtropical or tropical area where the infection is common. Exposure to repeated mosquito bites increases the risk. Persons with occasional, short visits to tropical or subtropical countries with a history of the disease are at very low risk. There have been no reported cases originating in the United States in recent years. Additional risk factors include lack of access to sanitary conditions and healthcare, having an occupation that requires one to work outside at night, living in an environment hospitable to mosquitoes, and having a compromised immune system.
Symptoms
The worm that causes filariasis damages the lymph system. Persons who are infected may have no symptoms or may never develop clinical symptoms. Lymphedema, or lymph fluid collection in the tissues, is the primary symptom. Lymphedema is swelling that maybe seen in the legs, arms, breasts, and genitalia. Swelling of the scrotum in men may occur due to infection with one of the causative worms. There is a decreased function of the lymph system, making it difficult for the body to fight infection. Hardening of the skin from bacterial infection may also be a symptom. In Asia, pulmonary filarial infection may cause a cough, wheezing, and difficulty breathing.
Additional symptoms and complications of filariasis exist as well. Acute adenolymphangitis is an inflammatory reaction to worms and their offspring which may cause fever, pain, chills, and redness around the infected lymph node. Chyluria is a complication of filariasis in which lymph fluid leaks into urine. Tropical pulmonary eosinophilia is a reaction to filarial worm antigens, which raises the white blood cell count and causes secondary infection symptoms. The lymphedema and elephantiasis that often accompany filariasis can cause mental health issues as well.
Screening and Diagnosis
There is no screening test for filariasis. The diagnosis is made with a blood smear stained and viewed under a microscope. The microfilariae circulate in the blood at night, so blood collection is more accurate when done at night. A serology test for immunoglobulin G4 may show elevated levels. Laboratory tests may be negative because lymphedema symptoms may occur many years after infection. Antigen tests can test for specific antigens released by the filarial worms. Polymerase Chain Reaction (PCR) tests, ultrasonography, and testing for a high eosinophil count in the bloodstream are also effective.
Treatment and Therapy
Certain drugs may be used to kill the microfilariae and the adult worms. These include diethylcarbamazine, albendazole, ivermectin, and doxycycline. However, drugs are not used if clinical symptoms such as lymphedema are present because an active infection is rarely present. A lymphedema therapist will provide help with skin care, exercise, and treatments to manage symptoms. Surgery may be indicated for infection of the scrotum.
Prevention and Outcomes
To prevent infection, people should avoid mosquito bites in tropical and subtropical areas by sleeping in an air-conditioned room or under a mosquito (sleeping) net, wearing long sleeves and pants, and using mosquito repellent, especially between dusk and dawn.
Bibliography
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Jong, Elaine C., and Russell McMullen, editors. Travel and Tropical Medicine Manual. 4th ed., Philadelphia:Saunders/Elsevier, 2008.
Lu, S., et al. "Localized Lymphedema (Elephantiasis): A Case Series and Review of the Literature." Journal of Cutaneous Pathology, vol. 36, 2009, pp. 1-20.
"Lymphatic Filariasis." Pan American Health Organization, www.paho.org/en/topics/lymphatic-filariasis. Accessed 30 Sept. 2024.
McDowell, Julie, and Michael Windelsprecht. The Lymphatic System. Santa Barbara, Calif.: Greenwood Press, 2004.
Marquardt, William C., editor. Biology of Disease Vectors. 2d ed., New York: Academic Press/Elsevier, 2005.
Muller, Ralph. Worms and Human Disease. 2d ed., New York: CABI, 2002.
Pastor, Ana Flávia, et al. "Recombinant Antigens Used as Diagnostic Tools for Lymphatic Filariasis." Parasites & Vectors, vol. 14, no. 1, 2021, p. 474, doi.org/10.1186/s13071-021-04980-3. Accessed 30 Sept. 2024.